Private branch exchanges (PBXs) are private telephone switching systems commonly found on a user's premises with an attendant console. PBXs are usually connected to a common group of lines from a public switching telephone network (PSTN) to provide service to a number of individual phones, such as in a business office. Users of the PBX share a certain number of outside lines for making telephone calls external to the PBX; such an arrangement is used because it is much less expensive than providing a direct external telephone line to every telephone in the organization.
In addition to PBXs, over the last decade there has been a marked increase in the use of media applications related to voice information. Voice mail is the best known example of a media application, but there are others as well, such as Automated Attendants, Interactive Voice Response systems that provide information or services to callers (e.g., Phone Banking), Automatic Call Distributor (ACD) systems etc. In the business setting, businesses have coupled media applications with their PBX systems. The traditional way of adding media capability to a PBX has been to attach a separate physical device (e.g., a hardware device) to the PBX for each desired media application. Thus, to add voicemail to a PBX, the PBX's owner had to attach a separate voicemail device to the PBX. This was a serious inconvenience for the owners of the PBX, since it was difficult and expensive to add media applications to their PBX. These separate devices also used up physical extensions or ports from the PBX as they had to be connected to the PBX. Aside from the costs, there are other inconveniences as well. Each media application required different software to be able to connect to PBX's made by different manufacturers. This resulted in integration problems and incompatibilities between the two systems. Additionally, because each media application was a different piece of hardware, the media applications either could not communicate with each other at all or, if they could communicate, needed to do so using the PBX as an intermediary, and thus tying up valuable lines for their own communication.